Sealing lids on containers by melting container material onto a thin metal foil membrane closing the container is known in the art as evidenced by U.S. Pat. No. 4,004,941 issued to D. Knudsen Aug. 30, 1977. Several problems result. This, in effect two lids are required, increasing container costs particularly in view of the problems of handling and quality control imposed by the fragile nature of the film and the inefficiencies of induction heating the metal foil in areas other than those being fused. Also, the large area foil may interfere or be inconsistent with microwave sterilization of the contents inside the container, which need be passed through only transparent to electromagnetic energy package areas such as plastic sidewalls.
Sterilization of food in sealed containers, such as by microwave energy, has associated problems because of generation of steam and handling of pressure, such as treated in the U.S. Patents, as follows:
J. Lundy, U.S. Pat. No. 3,215,539, Nov. 2, 1965, requires sealing the food in a vapor tight package of constant volume before directing microwave energy thereinto.
M. Beauvais et al. U.S. Pat. No. 4,406,860, Sept. 27, 1983, encloses a container within an outer pressure control jar with a steam release valve when sterilizing with microwaves and thereafter during cooling, in order to vacuum pack the food by pressure sealing of a lid into place by internal vacuum pressure of the container when the outer jar is opened to the atmosphere.
Clearly the prior art does not provide an inexpensive hermetically sealable container in which food can be quickly, reliably and inexpensively sterilized while sealing the lid on the container.
Another problem with prior art sealed plastic containers is the eventual unsealing or removal of the lid, which has led to the awkward and complex molds required for unusual and complex opening means as exemplified, for example, by U.S. Pats. Nos. 2,998,158 to E. Tupper, Aug. 29, 1961; 3,799,389 to S. Bloeck, Mar. 26, 1974 and 4,474,304 to S. Jacobs, Oct. 2, 1984. Thus, in heat sealed plastic containers, plastic tear strips or inserted tear threads are provided conventionally to remove the plastic lid from the plastic container body to which it is sealed. However, the opening process is tedious and time consuming rather than a simple pop off of the lid.
Accordingly it is a generaly objective of this invention to improve the state of the art by resolving the foregoing problems with a simplified container and sealing method therefor. Other objects, features and advantages of the invention will be found throughout the following description, drawings and claims.